Current limiting circuit of switching circuit and switching circuit

ABSTRACT

A current limiting circuit of a switching circuit, and a switching circuit are provided. The switching circuit uses a gallium nitride (GaN) power transistor as a main power transistor. The current limiting circuit includes a first terminal connected with a drain of the GaN power transistor, and a second terminal connected with a controller of the switching circuit. The current limiting circuit is configured to limit a current flowing out of a power supply terminal of the controller. The current limiting circuit suppresses a negative current flowing through the controller.

CROSS REFERENCE TO THE RELATED APPLICATIONS

This application is based upon and claims priority to Chinese PatentApplication No. 202110600543.7, filed on May 31, 2021, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to the field of power electronics, and inparticular, to a current limiting circuit of a switching circuit and aswitching circuit.

BACKGROUND

A pulse width modulation (PWM) control chip of a switching circuit canrealize high-voltage startup. Generally, there are two high-voltagepower obtaining methods. One is to supply power to a high-voltage pin ofa chip controller from an alternating current (AC) input terminalthrough a full wave rectifier circuit, and the other is to obtain powerfrom a direct current (DC) bus capacitor. If the control chip is anintegrated power metal-oxide-semiconductor field-effect transistor(MOSFET), as shown in FIG. 1 , the pins of the chip itself include adrain pin. In order to omit a high-voltage pin, for the high-voltagestartup power obtaining, power is usually taken from the drain pin.

The chip with the integrated power MOSFET can obtain power from thedrain pin, but if it is a chip integrated with a gallium nitride (GaN)power transistor, and a power is still obtained directly from the drainpin, there may be a relatively large negative voltage at a drainterminal of the chip, which affects the normal operation of the chip oreven damages it. This is because there is an important differencebetween device characteristics of the GaN power transistor and the powerMOSFET: an anti-parallel diode is integrated between a drain terminaland a source terminal of the power MOSFET, while the GaN powertransistor does not include such diode. In this case, a voltage drop ofthe GaN power transistor, when a reverse current flows, is much largerthan that of the power MOSFET, thereby causing the above problems.

SUMMARY

An objective of the present disclosure is to provide a current limitingcircuit limiting a negative current flowing through a controller of aswitching circuit and a switching circuit, which solves the problem inthe prior art that the negative current flows through the controller ofthe switching circuit due to the use of a GaN power transistor, whicheasily causes damage to the controller.

Based on the above objective, the present disclosure provides a currentlimiting circuit of a switching circuit. The switching circuit includesa main power transistor and a controller. A power supply terminal of thecontroller is connected with a drain of the main power transistor. Thecurrent limiting circuit includes a first terminal connected with thedrain of the main power transistor, and a second terminal connected withthe power supply terminal of the controller of the switching circuit.

Optionally, a GaN power transistor may be configured as the main powertransistor.

Optionally, the current limiting circuit may include a diode. The diodemay include an anode connected with the drain of the main powertransistor, and a cathode connected with the power supply terminal ofthe controller.

Optionally, the current limiting circuit may include a zener diode. Thezener diode may include an anode connected with the drain of the mainpower transistor, and a cathode connected with the power supply terminalof the controller.

Optionally, a breakdown voltage of the zener diode may be greater thanan absolute value of a drain-source voltage difference of the main powertransistor when a negative current flows through the main powertransistor.

Optionally, the current limiting circuit may include a main diode and aplurality of auxiliary diodes. The main diode may include an anodeconnected with the drain of the main power transistor, and a cathodeconnected with the power supply terminal of the controller.

The plurality of auxiliary diodes may be connected in anti-parallel withthe main diode after the plurality of auxiliary diodes are connected inseries.

Optionally, a number of the auxiliary diodes may be determined accordingto a source-drain voltage of the main power transistor.

Optionally, a total voltage drop of the plurality of auxiliary diodes inseries may be greater than an absolute value of a drain-source voltagedifference of the main power transistor when a negative current flowsthrough the main power transistor.

Optionally, the current limiting circuit may include a first resistor.The first resistor may include a first terminal connected with the drainof the main power transistor, and a second terminal connected with thepower supply terminal of the controller.

The present disclosure further provides a switching circuit, including amain power transistor and a controller. A power supply terminal of thecontroller is connected with a drain of the main power transistor, andthe switching circuit includes the current limiting circuit according toany one of the above items.

Optionally, the main power transistor may be a GaN main powertransistor.

Optionally, the main power transistor may be configured as an integratedpower chip including the GaN main power transistor and a driver of theGaN main power transistor.

Optionally, a common connection point of the power supply terminal ofthe controller and the drain of the main power transistor may beconnected to a power loop node of the switching circuit.

Compared with the prior art, the present disclosure has the followingadvantages: by connecting a current limiting circuit between a drain pinof the main power transistor and a high-voltage controller, a negativevoltage or negative current flowing to the controller is limited, suchthat the controller is prevented from bearing a large negative voltageor negative current, thereby avoiding the problem of abnormal operationof the controller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a switching circuit based on ametal-oxide-semiconductor (MOS) transistor in the prior art;

FIG. 2 is a schematic diagram of a switching circuit using Embodiment Iof a current limiting circuit according to the present disclosure;

FIG. 3 is a schematic diagram of a switching circuit using Embodiment IIof the current limiting circuit according to the present disclosure;

FIG. 4 is a schematic diagram of a switching circuit using EmbodimentIII of the current limiting circuit according to the present disclosure;and

FIG. 5 is a schematic diagram of a switching circuit using Embodiment IVof the current limiting circuit according to the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The preferred embodiments of the present disclosure are described indetail below with reference to the drawings, but the present disclosureis not limited to these embodiments. The present disclosure covers anysubstitution, modification, equivalent method and solution made withinthe spirit and scope of the present disclosure.

For a better understanding of the present disclosure, the specificdetails of the following preferred embodiments of the present disclosureare explained hereinafter in detail, while the present disclosure canalso be fully understood by those skilled in the art without thedescription of these details.

The present disclosure is described in detail by giving examples withreference to the drawings. It should be noted that the drawings aresimplified and do not use an accurate proportion, that is, the drawingsare for the objectives of conveniently and clearly assisting inillustrating embodiments of the present disclosure.

In an embodiment of the present disclosure, a GaN power transistor isused in a switching circuit as a main power transistor. A controller isconfigured to control an on-off state of the main power transistor. Apower supply terminal of the controller is connected with a drain of themain power transistor. The GaN power transistor and the controller areintegrated in a chip. A common connection terminal of the controller andthe GaN power transistor is used as a drain of the chip, that is, adrain terminal of the chip. A current flowing from the power supplyterminal of the controller to the drain of the main power transistor anda current flowing from a source of the main power transistor to itsdrain are defined herein as a negative current, and the power supplyterminal of the controller is an input terminal of a high-voltage powersupply of the controller. The current limiting circuit of the presentdisclosure limits the current flowing out of the power supply terminalof the controller, that is, limits the current flowing to the drain ofthe main power transistor.

As shown in FIG. 2 , a schematic diagram of a switching circuit usingEmbodiment I of a current limiting circuit according to the presentdisclosure is illustrated. The current limiting circuit includes a diodeD1. In order to ensure safe operation of the circuit, the diode D1 isusually configured as a high-voltage diode. The high-voltage diode D1includes an anode connected with the drain of the GaN power transistor,and a cathode connected with the power supply terminal of the controllerof the switching circuit. When the drain terminal of the GaN powertransistor is under a negative voltage, the diode D1 is off, and thecurrent is blocked from flowing out of the power supply terminal of thecontroller by the diode D1, so as to ensure normal and safe operation ofthe controller.

As shown in FIG. 3 , a schematic diagram of a switching circuit usingEmbodiment II of the current limiting circuit according to the presentdisclosure is illustrated. The current limiting circuit includes a zenerdiode D1. The zener diode D1 includes an anode connected with the drainof the GaN power transistor, and a cathode connected with the powersupply terminal of the controller of the switching circuit. A breakdownvoltage of the zener diode is greater than an absolute value of adrain-source voltage difference of the main power transistor when anegative current flows through the main power transistor. When there isa negative current in the system, the breakdown voltage of the zenerdiode D1 is greater than a source-drain voltage of the GaN powertransistor, the zener diode will not be broken down, so that the zenerdiode blocks the current from flowing out of the power supply terminalof the controller, to ensure normal and safe operation of thecontroller.

As shown in FIG. 4 , a schematic diagram of a switching circuit usingEmbodiment III of the current limiting circuit according to the presentdisclosure is illustrated. The connection relationship of the switchingcircuit is the similar to that in Embodiment I. However, the currentlimiting circuit includes a main diode D1 and a plurality of auxiliarydiodes. The main diode includes an anode connected with the drain of theGaN power transistor, and a cathode connected with the power supplyterminal of the controller. The plurality of auxiliary diodes areconnected in series and then connected in anti-parallel with the maindiode. The function of a string of the auxiliary diode is that when thedrain voltage of the GaN power transistor varies from high to low, awithstand voltage bore by the main diode D1 may just be a sum of voltagedrops Vf of a string of the auxiliary diodes, such that a low-voltagediode can be selected as the main diode D1.

In one embodiment, the number of a string of the auxiliary diodes isalso determined by a source-drain voltage Vsd of the GaN powertransistor. When there is a negative current in the system, the sum ofthe voltage drops Vf of a string of the auxiliary diodes is greater thanthe source-drain voltage Vsd of the GaN power transistor, such that whenthere is a negative current in the system, current always flows throughthe GaN power transistor, but no current will flow out of the powersupply terminal of the controller, so as to ensure normal operation ofthe controller. Through this method, a low-voltage diode can be selectedas the mentioned diode in every circumstance, which is convenient fordesign.

As shown in FIG. 5 , a schematic diagram of a switching circuit usingEmbodiment IV of the current limiting circuit according to the presentdisclosure is illustrated. The current limiting circuit includes a firstresistor. A resistor is connected in series between the drain pin of thechip and the high-voltage (HV) input terminal of the controller, thatis, the power supply terminal. When there is a reverse current in thesystem, for example, the voltage of the drain pin is about −2 V, anelectrostatic discharge (ESD) diode of the HV input terminal of thecontroller to the ground is turned on, and the voltage at the HV inputterminal is the voltage drop of the ESD diode, about 0.7 V. The voltageat the HV input terminal is negative at this time, however, throughlimiting the current of the resistor R connected in series, the majorityof the reverse current of the system flows through the path where theGaN power transistor is located, and the reverse current flowing throughthe controller is only (2-0.7 V)/R. Usually the resistor R is a few kohms, which does not affect normal high-voltage start-up charging. Atthe same time, the negative current of the controller may be effectivelysuppressed, and the negative voltage at the HV input terminal may alsobe limited, which is only about -0.7 V.

Although the embodiments are separately illustrated and described above,the embodiments contain some common technologies. Those skilled in theart can replace and integrate the embodiments. Any content not clearlyrecorded in one of the embodiments may be determined based on anotherembodiment where the content is recorded.

The embodiments described above do not constitute a limitation on thescope of protection of the technical solution of the present disclosure.Any modification, equivalent replacement, and improvement made withinthe spirit and principle of the above-mentioned embodiments shall fallwithin the scope of protection of the technical solution of the presentdisclosure.

What is claimed is:
 1. A current limiting circuit of a switchingcircuit, wherein the switching circuit comprises a main power transistorand a controller, a power supply terminal of the controller is connectedwith a drain of the main power transistor, and the current limitingcircuit comprises a first terminal connected with the drain of the mainpower transistor, and a second terminal connected with the power supplyterminal of the controller.
 2. The current limiting circuit according toclaim 1, wherein a gallium nitride (GaN) power transistor is configuredas the main power transistor.
 3. The current limiting circuit accordingto claim 2, comprising a diode, wherein the diode comprises an anodeconnected with the drain of the main power transistor, and a cathodeconnected with the power supply terminal of the controller.
 4. Thecurrent limiting circuit according to claim 2, comprising a zener diode,wherein the zener diode comprises an anode connected with the drain ofthe main power transistor, and a cathode connected with the power supplyterminal of the controller.
 5. The current limiting circuit according toclaim 4, wherein a breakdown voltage of the zener diode is greater thanan absolute value of a drain-source voltage difference of the main powertransistor when a negative current flows through the main powertransistor.
 6. The current limiting circuit according to claim 2,comprising a main diode and a plurality of auxiliary diodes, wherein themain diode comprises an anode connected with the drain of the main powertransistor, and a cathode connected with the power supply terminal ofthe controller; and the plurality of auxiliary diodes are connected inanti-parallel with the main diode after the plurality of auxiliarydiodes are connected in series.
 7. The current limiting circuitaccording to claim 6, wherein a number of the plurality of auxiliarydiodes is determined according to a source-drain voltage of the mainpower transistor.
 8. The current limiting circuit according to claim 6,wherein a total voltage drop of the plurality of auxiliary diodes inseries is greater than an absolute value of a drain-source voltagedifference of the main power transistor when a negative current flowsthrough the main power transistor.
 9. The current limiting circuitaccording to claim 2, comprising a first resistor, wherein the firstresistor comprises a first terminal connected with the drain of the mainpower transistor, and a second terminal connected with the power supplyterminal of the controller.
 10. A switching circuit, comprising a mainpower transistor and a controller, wherein a power supply terminal ofthe controller is connected with a drain of the main power transistor,and the switching circuit comprises the current limiting circuitaccording to claim
 1. 11. The switching circuit according to claim 10,wherein the main power transistor is a GaN main power transistor. 12.The switching circuit according to claim 10, wherein the main powertransistor is configured as an integrated power chip comprising a GaNmain power transistor and a driver of the GaN main power transistor. 13.The switching circuit according to claim 10, wherein a common connectionpoint of the power supply terminal of the controller and the drain ofthe main power transistor is connected to a power loop node of theswitching circuit.
 14. The switching circuit according to claim 11,wherein the current limiting circuit comprises a diode, wherein thediode comprises an anode connected with the drain of the main powertransistor, and a cathode connected with the power supply terminal ofthe controller.
 15. The switching circuit according to claim 11, whereinthe current limiting circuit comprises a zener diode, wherein the zenerdiode comprises an anode connected with the drain of the main powertransistor, and a cathode connected with the power supply terminal ofthe controller.
 16. The switching circuit according to claim 15, whereina breakdown voltage of the zener diode is greater than an absolute valueof a drain-source voltage difference of the main power transistor when anegative current flows through the main power transistor.
 17. Theswitching circuit according to claim 11, wherein the current limitingcircuit comprises a main diode and a plurality of auxiliary diodes,wherein the main diode comprises an anode connected with the drain ofthe main power transistor, and a cathode connected with the power supplyterminal of the controller; and the plurality of auxiliary diodes areconnected in anti-parallel with the main diode after the plurality ofauxiliary diodes are connected in series.
 18. The switching circuitaccording to claim 17, wherein a number of the plurality of auxiliarydiodes is determined according to a source-drain voltage of the mainpower transistor.
 19. The switching circuit according to claim 17,wherein a total voltage drop of the plurality of auxiliary diodes inseries is greater than an absolute value of a drain-source voltagedifference of the main power transistor when a negative current flowsthrough the main power transistor.
 20. The switching circuit accordingto claim 11, wherein the current limiting circuit comprises a firstresistor, wherein the first resistor comprises a first terminalconnected with the drain of the main power transistor, and a secondterminal connected with the power supply terminal of the controller.